Epoxy silane-imidazole treatment of reinforcement material

ABSTRACT

Reinforcement material intended for reinforced plastic applications is treated with an epoxy silane and then reacted with an imidazole or an admixture of an imidazole and the resin system to be reinforced.

United States Patent Green 51 Jan. 25, 1972 [5 EPOXY SILANE-IMIDAZOLE References Ciled REINFORCEMENT UNITED STATES PATENTS 2,946,701 7/1960 Plueddemann ..117/126 X Inventor: Harold Green, Haverwwn, 3,018,267 l/1962 Steckler ..117/126 X [73] Assigneez Air Pmduc's and Chemicals Inc" 3,438,937 4/1969 Christie ..260/309 X 1 Phllade phla Pa Primary ExaminerWi1liam D. Martin [22] F iled: Aug. 2, 1967 Assistant Examiner- David Cohen pp No 657 755 Attorney-B. Max Klevit and Barry Moyerman [57] ABSTRACT [52] 588 4 27 3; Reinforcement material intended for reinforced plastic appli- {17/138 cations is treated with an epoxy silane and then reacted with Int Cl C03c 25/02 B44d U an imidazole or an admixture of an imidazole and the resin 58 Field of Search ..1 17/26 0s, 26 G0, 26 0, 26 GR, System be remfmed' 117/76 T, 62.1, 62.2,138.8 N, 143 R, 53,145, 128.4; 260/309 10 Claims, N0 Drawings EPOXY SILANE-IMIDAZOLE TREATMENT OF REINFORCEMENT MATERIAL BACKGROUND OF THE INVENTION The present invention relates to the treatment of material which is used as reinforcement for resins. More particularly, this invention relates to the preparation of precatalyzed reinforcement material, such as filaments, by treatment of the material with epoxy silane and the subsequent reaction of the treated material with imidazole or an admixture of an imidazole and a synthetic resin.

It is common practice to use fibers of glass, cotton, asbestos, nylon, rayon, boron, etc., in random or woven form as reinforcement for resins. The purpose of such reinforcement is to increase the strength of the resins several fold. Since the resins are usually thick liquids which become hard when cured, they are typically combined with the reinforcement material, as well as a catalyst system, within a relatively short period before the resins are cured. Hence, the choice of catalyst is particularly important.

Filaments used for reinforcement are normally coated with a coupling agent or finishing material which makes the surface of the filaments substantive and compatible with the particular resin with which they are to be employed. The coupling agent is usually applied to the filaments during their formation. It is thus essential that the coupling agent become quickly and permanently anchored to the surface of reinforcement material and that the treated surface contain functional groups which participate in the further reaction with the resin system to be reinforced.

The filament reinforcement material, particularly glass filaments, can be used in various forms, including: filaments, strands (composed of a multitude of filaments), woven fabrics, nonwoven mattings, bulk chopped fibers, unidirectional rovings, etc. Fabrics are used where rather high strengths are required. Such fabrics range from 0.002 to 0.200 inch in thickness and can be tight or open woven. Most fabrics are balanced, i.e., they have almost equal amounts of fibers in each direction, but some are unidirectional having most of the fibers in one direction.

Nonwoven mattings are made of fiber strands laid in a random pattern. Various types are made, some with short lengths of fibers in a jackstraw pattern, some with swirls, continuous fibers, and some with fibers in a diamond type of pattern, in a variety of thicknesses. In order to hold the fibers together, a resinous binder can be employed. In some cases, the mats are stitched or needled, thus making the binder unnecessary.

Unidirectional reinforcements are continuous fibers in the fonn of yarns, rovings (which are untwisted, ropelike bundles of fibers), and beams (which are wide bands of parallel yarns). A variation of this is a nonwoven matting, where the fibers are essentially parallel and are held together by a resin binder. These reinforcements are used where strengths are requited in one direction only, as in a fishing rod. They give the highest strength of all reinforcements.

Rovings can also be chopped into short lengths for use in making preforrns, which are random fiber mats of complex shape. Chopped strands are available for preforming also. Most often, however, the chopped strands and the shorter milled fibers are used for incorporation into moulding compounds, premixed moulding putties, and potting compounds. Twisted strand is made according to conventional textile twisting techniques by removing the strand from the forming package and rewinding it.

Asbestos fibers are used in the form of woven fibers, felt and papers. In some cases, combinations of asbestos and glass fibers are used.

The other types of fibers are not always considered to be true reinforcements because the strengths they impart to the plastics is of a lower level than that of glass and asbestos. However, when intermediate strengths are satisfactory, they can be used. In this category are synthetic fibers such as nylon and rayon, and natural fibers such as cotton fabrics and paper.

Cotton and paper reinforcements have been widely used for years with phenolic and melamine resins for electrical and decorative panels. Sisal fibers are also a special case, because of their wide use as a low-strength reinforcement in premixed moulding compounds.

Surfacing and overlay mats are a type of semireinforcement used to give a smoother surface to moulded articles of reinforced plastics. These are thin veils of fine glass, nylon, rayon, or other fibers that are placed over the regular fabric, mat, or preformed reinforcement. Alpha cellulose paper also is sometimes used in applications such as this, to retain a high surface content of resin for a glossy finish.

Flake reinforcements of glass or mica are also of significance. They impart some strength and much stiffness, and increase the vapor-transmission resistance of mouldings.

Since there are many types of reinforced plastics, a wide difference in properties can be obtained. While there are at least parameters that affect the chemical, electrical, thermal and durability characteristics of reinforced plastic products, the following three are considered to be of major importance:

1. Choice of materials and process-particularly with respect to the reinforcement material, resin and curing agent;

2. Curing conditions; and

3. Bond of resin to reinforcement materialgovemed by the surface treatment of the reinforcement material and the intimacy of contact.

SUMMARY OF THE INVENTION It is an object of this invention to provide a method of applying a coupling agent and a catalyst system to reinforcement material which becomes readily and permanently attached to the reinforcement material by chemical reaction.

It is another object of this invention to provide a treatment for filaments which can be used to initiate subsequent curing of the resin system to be reinforced without the addition of a further catalyst system.

An additional object of this invention is to provide fiber roving treated with a coupling agent and catalyst which has good wet-out characteristics. It is particularly desirable in the formulation of glass fiber laminates that the resin completely impregnate the strand and wet the surfaces of the fibers as quickly as possible in order to reduce the time required to make the laminates as well as to provide a laminate with maximum possible strength.

It is yet another object of this invention to provide a precatalyzed fiber strand which can be twisted, plied and woven into cloth for use with a resin reinforcement without requiring further activation of the cloth prior to use.

These, and other objects, are accomplished by the practice of this invention which, briefly, comprises the initial treatment of reinforcement material with an epoxy silane and the subsequent reaction of the epoxy silane with an imidazole to provide a catalytically active surface which is capable of curing a resin system reinforced with the silane treated reinforcement material.

DESCRIPTION OF PREFERRED EMBODIMENT Any silane containing an epoxide group can be employed as the epoxy silane for the initial treatment of the glass fibers. Typical examples of such epoxy silanes are 3-glycidoxy-propyl trimethoxy silane; beta-3,4-epoxy cyclohexyl ethyl tn'methoxy silane and gamma glycidoxy propyl trimethoxy silane.

Preferred imidazole compounds to be used in the process of the invention are compounds having the formula:

wherein R R and R are independently selected from hydrogen, halogen or an organic radical, such as a hydrocarbon radical or a substituted hydrocarbon radical as an ester, ether, amide, amine, imine, halogen, or mercaptan substituted hydrocarbon radical. Especially preferred are the imidazoles wherein R,, R, and R stand for hydrogen or a hydrocarbon radical, and preferably an alkyl, alkenyl, cycloalkyl, cycloalkenyl, aryl, or arylalkyl radical and particularly alkyl radicals of l to 19 carbon atoms, arylhydrocarbon radicals of 6 to 14 carbon atoms and aralkyl hydrocarbon radicals of 7 to 16 carbon atoms.

Examples of such compounds include, among others, 2- methyl imidazole, 2-ethyl imidazole, 2-ethyl-4-methyl imidazole, 4-butyl-5-ethyl imidazole, 2-dodecyl-5-methyl imidazole, 2, 4, S-trimethyl imidazole, 2-cyclohexyl-4-methyl imidazole, 2-butoxy-4-allyl imidazole, 2-carbo-ethoxy butyl-4- methyl imidazole, 2-octyl-4-hexyl imidazole, 2-ethyl-4-phenyl imidazole, 2, S-diphenyl imidazole, Z-benzyl imidazole, 2- phenethyl imidazole, and mixtures thereof. Especially preferred are liquid imidazoles and particularly the alkyl substituted imidazoles wherein the alkyl groups contain not more than l2 carbon atoms each, either as individual compounds or mixtures thereof.

The resin system to be reinforced can be any synthetic material which is catalyzed by the described imidazole compound including phenolics, polyurethanes and polyepoxides. The invention is also useful when fibers are to be used as reinforcement for unsaturated polyester-ethylenic monomer resins which are interpolymers of (a) a polyester of a dihydric alcohol such as ethylene glycol, propylene glycol, l, 3-butylene glycol, diethylene glycol, dipropylene glycol and higher polymers of alkylene glycols and an alpha, beta ethylenic dicarboxylic acid such as maleic or fumaric acid with other dicarboxylic acids such as adipic, succinic, azelaic and phthalic acids and (b) a monomer, soluble in the polyester, containing a terminal ethylenic group, such as styrene, vinyl acetate, vinyl toluene, allyl esters including allyl acetate, allyl succinate, etc.

Epoxy resins are the preferred resin systems to be reinforced. Polyepoxides which can be used in the present invention are those compounds possessing on the average more than one epoxy or oxirane group per molecule. The number of epoxy groups contained in the average molecule is obtained by dividing the average molecular weight of the polyepoxide by the epoxide equivalent weight. The polyepoxides can be saturated or unsaturated, aliphatic, aromatic or heterocyclic, monomeric or polymeric and, if desired, can be substituted with noninterfering substituents such as halogen atoms, hydroxy groups and ether radicals.

Preferred polyepoxide compounds are glycidyl ethers of polyhydrie phenols, such as diphenylol alkanes, e.g., diphenylol propane, diphenylol ethane and diphenylol methane, diphenylol sulphone, hydroxyquinone resorcinol, dihydroxydiphenyl dihydroxynaphthalenes and polyhydric phenols, such as novolacs and resols, which have been repaired by condensation of phenol and formaldehyde.

Glycidyl ethers of polyhydric phenols can be prepared in various ways, for example, by reaction of the polyhydric phenol with epichlorohydrin in the presence of a base, such as sodium hydroxide or potassium hydroxide. Important polyepoxy compounds are the glycidyl ethers of 2,2-bis(4- hydroxy-phenyU-propane. The molecular weight, as well as the softening point and viscosity of such compounds, generally depend on the ratio of epichlorohydrin to 2,2-bis (4-hydroxyphenyl) propane. If a large excess of epichloro-hydrin is used, e.g., l molecules of epichlorohydrin per molecule of 2,2-bis (4-hydroxy phenyl) propane, the main component in the reaction product is a glycidyl ether or low molecular weight. In some instances, polyethers can contain small amounts of material with a terminal glycidyl radical in hydrated form. Glycidyl polyethers of 2,2-bis (4-hydroxyphenyl) propane having a molecular weight between 340 and 1,000 are preferred.

Other suitable polyepoxy compounds are poly(epoxyalkyl) ethers of aliphatic polyhydroxy compounds such as ethylene glycol, glycerol and trimethylolpropane; poly(epoxy alkyl) esters of polycarboxylic acids, such as the diglycidyl esters of phthalic acid, terephthalic acid and adipic acid, and

. polyglycidyl esters of polymer unsaturated fatty acids such as Resin Epoxide Approximate Viscosity Equivalent Molecular Wt.

Epon 812 -160 306 l-2 poise: Epon 826 -188 65-95 poise: Epon 828 -192 390 l00l60 pulses Epon 834 230-280 470 4-9 poises Epon l00l 425-550 .900 Solid Dow 33l I92 390 Other epoxy resins which can be used include epoxidized polyolefins and epoxidized polybutadiene.

Various combinations of epoxy resinsand phenol-aldehyde resins, urea-aldehyde resins, furfural resins, polyacetal resins, polycarbonate resins and polyamide resins can also be employed as a synthetic resin.

While the epoxy silane can be applied to strands of fibers, the epoxy silane is preferably applied to individual filaments prior to the time they are grouped together to form a strand. Any convenient method of applying the epoxy silane to the fibers can be employed, e. g., by means of a bath, roller, brush or pad applicator. The silane coupling agent immediately becomes permanently attached to the surface of the reinforcement material and produces the degree of strand integrity and hardness required for forming the strand into a woven cloth or woven roving. The amount of silane coupling agent applied onto the reinforcement material averages about 0.2 to 10.0 percent by weight, preferably at least about 0.75 percent by weight. Prior to the application of the epoxy silane or simultaneously with such application, conventional sizing agents can also be applied to the material.

The imidazole compound, with or without the resin to be reinforced, if then reacted with the epoxy silane to provide treated reinforced material containing active imidazole groups for catalytically curing the reinforced resin. The imidazole compound can be applied to the silane treated reinforcement material by means similar to that employed initially to apply the epoxy silane. The reaction between the imidazole and the epoxy silane is essentially stoichiometric. Preferably, the treated reinforcement material will contain between about 0.l and 25 parts of imidazole per 100 parts of the synthetic resin which is employed.

When the imidazole is applied to the reinforcement material prior to the addition of resin, the treated reinforcement material obtained by the initial epoxy silane-imidazole reaction can be stored indefinitely. In addition, filaments treated in this manner can be fabricated into the desired final product, including various textile products, such as twisted strand, cloth, chopped strand, chopped strand mat, roving and woven roving.

Following the addition of synthetic resin, with or without the simultaneous addition of imidazole, to the reinforcement material, the synthetic resin is cured merely by heating. The temperatures employed for curing can vary over a wide range. in general, temperatures ranging from 40 to 300 C. will give satisfactory results. Preferred temperatures range from 50 to 250 C.

Various additives can be included in the mixture before cure, such as solvents, diluents, dyes, resins, plasticizers and nonvolatile extenders. Suitable solvents include benzene, toluene, cyclohexane, ketones, ethers, esters, nitriles and the like. Monoepoxy diluents, such as butyl glycidyl ether, phenyl glycidyl ether and monoglycidyl esters can be employed when the synthetic resin to be reinforced is a polyepoxide. In such instances, the monoepoxy diluents can generally be used in amounts of up to 20 percent by weight of the polyepoxide. Nonreactive, nonvolatile extenders, such as coal tars, refined coal tars, coal tar pitches, asphalts, pine tar, pine oil, lube oil fractions and aromatic extracts thereof and lube oil raffinates can also be employed.

Other materials which can be included are pigments, stabilizers and reinforcing fillers, such as aluminum powder, zinc dust, and clay. These fillers are preferably used in amounts varying from to 200 parts per 100 parts by weight of the synthetic resin.

The resinified products obtained by the above-identified process of this invention have surprisingly high flexural strength and excellent retention of such strength after exposure to elevated temperature. These desirable characteristics are demonstrated by measurements made after exposure of the resinified products to dry heat or after extended immersion in boiling water. Coupled with the other desirable attributes of resin products of this type, such as solvent resistance and dimensional stability, highly useful materials are provided. These desirable properties make the process of particular value in the preparation of laminated articles and in filament winding applications.

In filament winding applications, precatalyzed reinforcement material treated in accordance with the present invention can be passed into and through the synthetic resin and then wound onto the desired mandrel or form and the formed unit allowed to cure by the application of heat. Since only moderately elevated temperatures are required for curing, curing can be accomplished in close proximity with heat-sensitive materials.

Pipe can also be made by centrifugal casting, where resin and reinforcement material are placed inside a rapidly revolving form and then cured. Rods and bars are made by pulling treated yarns and rovings through a resin bath and forming die, followed by curing.

The invention will be illustrated by the following specific examples, it being understood that there is no intention to be necessarily limited by any details thereof since variations can be made within the scope of the invention.

EXAMPLE l 12 plies of 181 style glass fiber cloth were treated with 3- glycid-oxy-propyl trimethoxy silane by submerging the cloth in the epoxy silane. A mixture of 2-ethyl-4-methyl imidazole and Epon 826 was then applied to separate samples of the epoxy silane treated cloth at a resin pickup of 50 percent by weight to provide cloth having respectively, 2 PHR and l0 PHR of 2-ethyl-4-methyl imidazole per 100 parts of Epon 826.

Laminates, having a nominal thickness of about 0.125 inches, were then prepared from the cloth at a pressure of 100 pounds per square inch for 30 minutes at 175 C. Post-curing was effected for 30 minutes at 204 C. The flexular modulus and flexular strength (ASTM-D-790) for the two laminates at 23 C. are shown in the following table:

Flexural strength (p.s.i.)

At 23 C.

after At 23 0.. 2 hours after 30 Imldazole concentrain boiling minutes tlon (phr.) At 23 C. water at 260 C.

Flexural Modulus (p.s.l.)

38X10 39X10 30x10 31X 10 As seen in the above table, the physical properties of the laminates were excellent with respect to hot strength.

EXAMPLE ll 12 plies of 181 style glass fiber cloth were treated with 3- glycid-oxy-propyl trimethoxy silane by submerging the cloth in the epoxy silane. 2-ethyl-4-methyl imidazole was then applied to the silane treated cloth followed by the subsequent addition of Epon 826 at a resin pickup of 50 percent by weight. The addition of 2-ethyl-4-methyl imidazole to the silane treated cloth provided 2 phr of 2-ethyl-4-methyl imidazole per 100 parts of the added Epon 826.

The laminate, having a nominal thickness of about 0.125 inches, was prepared from the cloth at a pressure of 100 pounds per square inch for 30 minutes at C. The material was then post-cured at 204 C. for 30 minutes. Flexural strength determinations (ASTM-D-790) were made at the conditions shown in the following table:

Condition Flexural Strength At 23 C. after 2 hrs. in boiling water 72,500

As seen by comparison of the above table with the table in example I, the flexural strength of the laminate prepared by sequential addition of epoxy silane, imidazole and polyepoxide is somewhat higher initially and after two hours in boiling water than the flexural strength of the laminate prepared by the initial reaction of an epoxy silane with the glass filaments followed by the subsequent reaction of the silane treated glass with a mixture of the imidazole and polyepoxide.

EXAMPLE Ill EXAMPLE IV Glass fiber cloth was treated with 3-glycidoxypropyl trimethoxy silane by submerging the cloth in the epoxy silane. Samples of the silane treated cloth were then separately treated with l phr of benzoyl peroxide and the following materials:

a. A styrene modified liquid polyester resin, prepared by reacting propylene glycol, maleic anhydride and phthalic anhydride having a styrene content of 33 percent by weight and a viscosity of 800 to 1000 cps. at 23 C. at a resin pickup of 50 percent by weight.

b. 2 phr of 2-ethyl-4-methyl imidazole and subsequently with the polyester identified in (a) at a resin pickup of 50 percent by weight.

Sample Flexural Strength (p.s.i.)

The resulting improvement in the flexural strength of the polyester glass cloth laminates with the incorporation of the imidazole compound can be seen. When heat cleaned glass was substituted for the silane treated glass in sample (c), the flexular strength of the resulting laminate at 23 C. was 21,500 p.s.i.

Obviously, many modifications and variations of the invention as hereinbefore set forth can be made without departing from the spirit and scope thereof and therefore only such limitations should be imposed as are indicated in the appended claims.

What is claimed is:

l. The method of treating material for use in the reinforcement of synthetic resins which comprises, treating fibrous reinforcement material with an epoxy silane and thereafter reacting the silane treated material with an imidazole having the formula wherein R R and R are independently selected from the group consisting of hydrogen, alkyl radicals of l to 19 carbon atoms, aryl hydrocarbon radicals of 6 to 14 carbon atoms and aralkyl radicals of 7 to 16 carbon atoms; and obtaining by said treatment and said reaction a surface coating on said reinforcement material which has catalytic activity for curing synthetic resins and promoting improved bonding to said epoxy silane.

2. The method of claim 1 wherein the amount of epoxy silane applied to the fibrous reinforcement material is between 0.2 and 10 percent by weight.

3. The method of claim 1 wherein the fibrous reinforcement material is selected from the group consisting of glass, cotton, asbestos, nylon, rayon and boron.

4. The method of claim 1 in which a synthetic resin is applied to the epoxy silane-imidazole treated fibrous reinforcement material and then cured at a temperature of between 40 and 300 C.

S. The method of claim 4 wherein the synthetic resin is cured at a temperature of between 50 and 250C.

6. The method of claim 4 wherein the amount of imidazole present on the epoxy silane-imidazole treated fibrous reinforcement material is between 0.1 and 25 parts per parts of synthetic resin.

7. The method of claim 6 wherein the fibrous reinforcement material is glass, the imidazole is 2-ethyl-4-methyl imidazole and the synthetic resin is a polyepoxide.

8. The method of treating material for use in the reinforcement of synthetic resins which comprises treating fibrous reinforcement material with an epoxy silane and thereafter apply ing to the silane-treated reinforcement material a synthetic resin having incorporated therein an imidazole having the formula wherein R R and R are independently selected from the group consisting of hydrogen, alkyl radicals of one to 19 carbon atoms, aryl hydrocarbon radicals of six to l4 carbon atoms and aralkyl radicals of seven to 16 carbon atoms, and then curing the synthetic resin at a temperature of between 40 and 300 C.

9. The method of claim 8 wherein the synthetic resin is cured at a temperature between 50 and 250 C.

10. The method of claim 8 wherein the amount of imidazole present is between 0.1 and 25 parts per 100 parts of synthetic resin. 

2. The method of claim 1 wherein the amount of epoxy silane applied to the fibrous reinforcement material is between 0.2 and 10 percent by weight.
 3. The method of claim 1 wherein the fibrous reinforcement material is selected from the group consisting of glass, cotton, asbestos, nylon, rayon and boron.
 4. The method of claim 1 in which a synthetic resin is applied to the epoxy silane-imidazole treated fibrous reinforcement material and then cured at a temperature of between 40* and 300* C.
 5. The method of claim 4 wherein the synthetic resin is cured at a temperature of between 50* and 250* C.
 6. The method of claim 4 wherein the amount of imidazole present on the epoxy silane-imidazole treated fibrous reinforcement material is between 0.1 and 25 parts per 100 parts of synthetic resin.
 7. The method of claim 6 wherein the fibrous reinforcement material is glass, the imidazole is 2-ethyl-4-methyl imidazole and the synthetic resin is a polyepoxide.
 8. The method of treating material for use in the reinforcement of synthetic resins which comprises treating fibrous reinforcement material with an epoxy silane and thereafter applying to the silane-treated reinforcement material a synthetic resin having incorporated therein an imidazole having the formula wherein R1, R2 and R3 are independently selected from the group consisting of hydrogen, alkyl radicals of one to 19 carbon atoms, aryl hydrocarbon radicals of six to 14 carbon atoms and aralkyl radicals of seven to 16 carbon atoms, and then curing the synthetic resin at a temperature of between 40* and 300* C.
 9. The method of claim 8 wherein the synthetic resin is cured at a temperature between 50* and 250* C.
 10. The method of claim 8 wherein the amount of imidazole present is between 0.1 and 25 parts per 100 parts of synthetic resin. 